The invention concerns a system for producing steel, which comprises a vessel, in which the metallic charge is melted, oxidized, and refined, with an upper vessel section with at least one opening, through which at least one electrode can be lowered into the vessel, and with a lower vessel section with a vessel bottom, and means for tapping the melt and slag from the vessel.
In the production of steels, especially high-grade steels, such as chromium-containing, stainless, acid-resistant, and heat-resistant steels, the charge is usually melted in an electric arc furnace and then oxidized in a separate converter. In a system of this type, the arc furnace serves as the premelting unit, and the actual process of oxidizing and refining to produce the desired grade of steel is carried out in the converter.
DE 197 28 102 A1 describes a system for carrying out both of these processes, i.e., melting and oxidizing, in a single vessel. A vessel suitable for this purpose has a bulging middle and lower section, which is mounted on a tiltable trunnion ring, as is customary in previously known converter systems. Melt and slag are tapped into the steel pouring ladle, which is located at ground level, by tilting the vessel about the center axis and by means of tapping connections or tapholes.
A trunnion ring of this type, its mounting, and the necessary equipment for tilting the vessel by means of the trunnion ring are expensive to design and install and require extensive drive and control equipment. In addition, a vessel of this type with a trunnion ring requires a secure foundation or a secure furnace platform, whose construction consumes a great deal of space and energy.
Proceeding from this general state of the art, the goal of the invention is to develop a generic system which retains the combined melting and oxidizing functions of the system and at the same time simplifies its structural design.
This goal is achieved by the system with the features specified in claim 1. Advantageous modifications are disclosed in the subclaims.
In accordance with the invention, it is proposed that, instead of the previously known tapping system, in which the vessel, which is equipped with tapping connections and is held by a trunnion ring and tilted about its axis to tap slag and melt, a bottom tapping system be provided for tapping the melt and possibly the slag into a collecting vessel located below the vessel in the untilted normal position of the vessel.
At the same time, since it is not desirable to completely abandon the tilting motion, which is useful, especially as a rocking or tilting motion of the molten bath at small tilting angles around the normal position, preferably less than xc2x15xc2x0, at the end of the melting operation, it is proposed that the system be designed with a tilting system with a single-piece or multiple-piece tilting frame, which is located at the level of the bottom of the vessel and on which the vessel can be set by lowering the bottom of the vessel into it.
The tilting system is provided with a tilting element, which acts on the frame on one side, preferably by a lifting motion, in such a way that the frame and thus the vessel are shifted into a tilting motion. The tilting system is also provided with a bearing element, which is located opposite the tilting element, for absorbing the tilting motion of the vessel. The bearing element has either a single-piece design or a multiple-piece design.
All together, due to the proposed bottom tapping system, it is possible to eliminate the conventional, expensive, tilting equipment with a trunnion ring, which comprises the bulging middle section of the melting and oxidizing vessel, and the corresponding drive and control equipment that it requires. This makes it possible to achieve a vessel with an overall structurally simplified design and thus lower installation expense. Due to the elimination of the trunnion ring, the requirements and thus the costs for the furnace platform or the foundation are reduced. However, the possibility of tilting the vessel is still made available by simple mechanical means (preferably with a tilting frame operated with one or more hydraulic tilting cylinders). However, as an alternative to this solution involving the use of a tilting frame, it is also perfectly conceivable for the vessel to be moved horizontally a short distance along a track by means of hydraulic cylinders to produce the tilting motion.
In order to ensure position control of the vessel both in the first embodiment of the vessel with a bottom tapping system, but without a tilting system, and in the second embodiment of the vessel with a tilting system, the lower section of the vessel has laterally displaced or reinforced wall regions above the bottom of the vessel to form stable bearing surfaces, which either rest on bearing supports mounted along the circumference of the vessel or rest directly on the tilting frame. The bearing supports are mounted either directly on the furnace platform or the foundation or on the tilting frame.
The system described, for example, in WO 97/18,050 could possibly apply to the proposed bottom tapping system. However, the object of the invention is not limited to a bottom tapping system of this type, but rather all types of known bottom tapping systems are conceivable. In accordance with the invention, bottom tapping systems are proposed, whose tap openings may be arranged either centrically or eccentrically to the vertical center axis of the vessel.
Basically, it is possible to tap both the melt and the slag successively in a casting after the oxidizing operation by means of the proposed bottom tapping system in the untilted normal position of the vessel of xc2x10xc2x0. In addition, a slag-tapping system with a movable slag gate in the side wall of the vessel is proposed, in which the slag is tapped by moving the vessel by means of the tilting system out of the normal position of xc2x10xc2x0 and into a slag-removal position of preferably up to xe2x88x925xc2x0.
The vessel is located on a furnace platform in the form of a steel structure, on a foundation or preferably on the tilting frame, either permanently or as an interchangeable vessel, so that shut-down time due to relining, maintenance work, or repairs can be reduced by replacing the vessel with another vessel.
All together then, there are embodiments of a stationary or tiltable vessel system that is permanently installed and embodiments of a stationary or tiltable vessel system that allows vessel change.
During the melting process, the vessel is provided with a furnace root, which is preferably water-cooled. The opening in the furnace roof for holding the electrodes can be variously designed, depending on whether the heating equipment for inserting the electrodes is rigidly installed on the furnace platform or foundation or is installed on the tilting frame of the tilting system and thus also participates in the tilting or rocking motion. In the first type of embodiment, the opening must be enlarged relative to the circumference of the electrodes, which are held by an electrode jib arm and are inserted from above into the opening in the vessel by means of a swivelling device of the heating equipment. This enlargement is necessary to ensure that the electrodes do not strike the wall of the opening when the vessel is tilted. If the heating equipment and thus the equipment that supports the electrodes participates in the motion, the electrode openings can be made suitably smaller.
However, still another important advantage is gained by providing the vessel with a roof or hood that can be swung out of the way or, alternatively, with a roof or hood that can be moved horizontally after it has been lifted slightly. Compared to the vessel described in DE 197 28 102 A1, the distance the electrodes must be raised is much smaller, because the electrodes are moved out with the converter hood swung out or moved aside. Since the electrodes must be swung out or moved aside only over the edge of the vessel, the distance the electrodes must be raised is much smaller than in the case of the previously known vessel, in which the electrodes must be raised above the cylindrical section of the vessel, which is lengthened due to the deslagging operation.
Finally, a twin-furnace system is proposed, which has two of the vessels or systems proposed in accordance with the invention, in each of which either the melting phase or converter phase is occurring at any given time. Different roof systems are used in these different phases. In the melting phase, a largely water-cooled furnace roof in tubular construction is preferably used, i.e., pipelines arranged parallel to one another, through which cooling water flows (in-pipe-to-pipe or pipe-gap-pipe design), whereas in the converter phase, a hood that consists of water-cooled refractory concrete is suitable.
Additional advantages and features of the invention are described below with reference to the specific embodiments shown in the attached drawings.
FIG. 1a shows a cross section of a first embodiment of the proposed system for arc furnace operation.
FIG. 1b shows a cross section of a first embodiment of the proposed system for converter operation.
FIG. 2a shows a cross section of a second embodiment of the proposed system with a tilting system for arc furnace operation.
FIG. 2b shows a cross section of a second embodiment of the proposed system with a tilting system for converter operation.
FIG. 3 shows a cross section of a third embodiment of the proposed system with reinforced vessel bottom and tilting system.
FIG. 4 shows a top view of a twin-furnace system with two systems in accordance with the invention arranged side by side.
FIG. 5a shows a section along the line Xxe2x80x94X in FIG. 2a of a one piece tilting frame.
FIG. 5b shows a section along the line Xxe2x80x94X in FIG. 2a of a multi-piece tilting frame.